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Message-Id: <a0d2d13698ea27f671a077c9f47b7ce855054a47.1307040443.git.mika.westerberg@iki.fi>
Date: Thu, 2 Jun 2011 21:59:38 +0300
From: Mika Westerberg <mika.westerberg@....fi>
To: netdev@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, kernel@...tstofly.org,
hsweeten@...ionengravers.com, ryan@...ewatersys.com,
Mika Westerberg <mika.westerberg@....fi>
Subject: [PATCH v2 5/5] net: ep93xx_eth: fix DMA API violations
Russell King said:
>
> So, to summarize what its doing:
>
> 1. It allocates buffers for rx and tx.
> 2. It maps them with dma_map_single().
> This transfers ownership of the buffer to the DMA device.
> 3. In ep93xx_xmit,
> 3a. It copies the data into the buffer with skb_copy_and_csum_dev()
> This violates the DMA buffer ownership rules - the CPU should
> not be writing to this buffer while it is (in principle) owned
> by the DMA device.
> 3b. It then calls dma_sync_single_for_cpu() for the buffer.
> This transfers ownership of the buffer to the CPU, which surely
> is the wrong direction.
> 4. In ep93xx_rx,
> 4a. It calls dma_sync_single_for_cpu() for the buffer.
> This at least transfers the DMA buffer ownership to the CPU
> before the CPU reads the buffer
> 4b. It then uses skb_copy_to_linear_data() to copy the data out.
> At no point does it transfer ownership back to the DMA device.
> 5. When the driver is removed, it dma_unmap_single()'s the buffer.
> This transfers ownership of the buffer to the CPU.
> 6. It frees the buffer.
>
> While it may work on ep93xx, it's not respecting the DMA API rules,
> and with DMA debugging enabled it will probably encounter quite a few
> warnings.
This patch fixes these violations.
Signed-off-by: Mika Westerberg <mika.westerberg@....fi>
Acked-by: Russell King <rmk+kernel@....linux.org.uk>
---
drivers/net/arm/ep93xx_eth.c | 19 +++++++++++++------
1 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/drivers/net/arm/ep93xx_eth.c b/drivers/net/arm/ep93xx_eth.c
index 56b51a1..c2a7847 100644
--- a/drivers/net/arm/ep93xx_eth.c
+++ b/drivers/net/arm/ep93xx_eth.c
@@ -285,11 +285,14 @@ static int ep93xx_rx(struct net_device *dev, int processed, int budget)
skb = dev_alloc_skb(length + 2);
if (likely(skb != NULL)) {
+ struct ep93xx_rdesc *rxd = &ep->descs->rdesc[entry];
skb_reserve(skb, 2);
- dma_sync_single_for_cpu(ep->dma_dev,
- ep->descs->rdesc[entry].buf_addr,
+
+ dma_sync_single_for_cpu(ep->dma_dev, rxd->buf_addr,
length, DMA_FROM_DEVICE);
skb_copy_to_linear_data(skb, ep->rx_buf[entry], length);
+ dma_sync_single_for_device(ep->dma_dev, rxd->buf_addr,
+ length, DMA_FROM_DEVICE);
skb_put(skb, length);
skb->protocol = eth_type_trans(skb, dev);
@@ -351,6 +354,7 @@ poll_some_more:
static int ep93xx_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct ep93xx_priv *ep = netdev_priv(dev);
+ struct ep93xx_tdesc *txd;
int entry;
if (unlikely(skb->len > MAX_PKT_SIZE)) {
@@ -362,11 +366,14 @@ static int ep93xx_xmit(struct sk_buff *skb, struct net_device *dev)
entry = ep->tx_pointer;
ep->tx_pointer = (ep->tx_pointer + 1) & (TX_QUEUE_ENTRIES - 1);
- ep->descs->tdesc[entry].tdesc1 =
- TDESC1_EOF | (entry << 16) | (skb->len & 0xfff);
+ txd = &ep->descs->tdesc[entry];
+
+ txd->tdesc1 = TDESC1_EOF | (entry << 16) | (skb->len & 0xfff);
+ dma_sync_single_for_cpu(ep->dma_dev, txd->buf_addr, skb->len,
+ DMA_TO_DEVICE);
skb_copy_and_csum_dev(skb, ep->tx_buf[entry]);
- dma_sync_single_for_cpu(ep->dma_dev, ep->descs->tdesc[entry].buf_addr,
- skb->len, DMA_TO_DEVICE);
+ dma_sync_single_for_device(ep->dma_dev, txd->buf_addr, skb->len,
+ DMA_TO_DEVICE);
dev_kfree_skb(skb);
spin_lock_irq(&ep->tx_pending_lock);
--
1.7.4.4
--
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